connectable

Hi,
Many thanks for your thorough and informative review. In a difficult year, and with two of my development machines failing, I rashly bought 3 4Gb Pi-400s and 2 of the pi keyboard/hub units.
I too, had problems with under-voltage on both machines. Fortunately, I have installed an uninterruptible DC 14v ring in my house, and use DC-DC converters to step the voltage down to around 5.3, for these machines, which as you have noted, gets around the problem. As for the keyboard? All 5 of the keyboards have at least one consistent problem - 'h' key, and lesser so, some of the number keys.
By far the worst problem, and one which you haven't mentioned, is during editing - particularly cut & paste using the mouse. I'm using 'Buster', and no editor is safe, whether it is geany, Thonny, Visual Studio or editing a WordPress post. 'cut sections get dropped into inappropriate places in a file or in BOTH files if I'm transferring from one to the other. The only 'safe' option is VIM, which points very strongly to the mouse and/or it's driver.
raspberry.pi.org have apparently lost the plot. There are other issues, especially with the Raspian OS'es. The last decent version of Raspbian was jessie. Everything after it is a mess.
My main development focus is on monitoring and control, and this includes website development, backend server, plus wifi-connected slaves such as the pi-zero, and latterly WEMOS D1.
Your review has prompted me to do two things: 1 - try Manjaro on thhe Pi400's, and 2: examine using Armbian on an Odroid XU4 which is currently unemployed.
Many thanks again NicoD.